High-frequency power supply circuit

ABSTRACT

To accurately regulate output of a high-frequency power with a simple configuration. A high-frequency power supply circuit includes: a basic drive square wave generation circuit unit ( 5 ) for generating a basic drive square wave having an output frequency; a differential signal generation circuit unit ( 9 ) for generating a front edge differential signal of the basic drive square wave; a vibrator circuit unit ( 15 ) having a square wave signal generator ( 10 ) for outputting a square wave signal having a signal width within a period corresponding to a half cycle of the output frequency upon input of a trigger signal from outside and signal width control circuits ( 11, 12 ) varying/controlling the signal width of the square wave signal according to the control signal; and a switching amplification circuit unit ( 6 ) for amplifying the amplification source signal based on the output signal from the vibrator circuit unit ( 15 ). The front edge differential signal generated by the differential signal generation circuit unit ( 9 ) is made to be a trigger signal in the vibrator circuit unit ( 15 ).

TECHNICAL FIELD

The present invention relates to a high-frequency power supply circuitused in a high-frequency power supply apparatus or the like forsupplying high-frequency power to a plasma generator or the like.

BACKGROUND ART

In conventional practice, high-frequency power supply circuits used inhigh-frequency power supply apparatuses or the like for supplyinghigh-frequency power to plasma generators or the like use linearamplifiers connected in multiple stages so that minute vibrations ininternal liquid crystal oscillators are amplified to the final output.Such amplifiers use an amplification scheme known as linearamplification, which is an amplification scheme having a comparativelylow efficiency of about 50%.

However, as semiconductor wafers and display panels or the like havingtransistors incorporated therein have both increased in size, plasmatreatment apparatuses have also increased in size, and greater outputshave been required for the power sources for the plasma. In conventionallow-efficiency amplifiers, the volume and lost power increasedramatically with increased output, and commercial demand has thereforenot been satisfied. High-frequency power sources that use anamplification scheme known as switching-mode amplification and providedwith higher efficiency (80% or more) than in the prior art have recentlybeen put into use.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, since switching-mode amplification involves the application ofPWM techniques, it is believed that the output power of thehigh-frequency power source is controlled by controlling the pulse width(duty). In conventional practice, however, methods implemented usingthyristor-based firing control are used to control the pulse width(duty) as shown in FIG. 5, for example, but the pulse width that can becontrolled in such thyristor-based firing control must have a frequencyof about several hundred kilohertz. If the frequency supplied from thehigh-frequency power source is comparatively high, such as in themegahertz range, which is greater than several hundred kilohertz andwhich may, for example, be 13.56 MHz, the pulse is narrow as such, andit is difficult to control the output power of the high-frequency powersource by controlling the pulse width. Therefore, the high-frequencyoutput power of a high-frequency power source is controlled by keepingthe amplified pulse width constant and controlling (increasing andreducing) the drive voltage used in this amplification to control theoutput power. In this case, the time difference until the output powerchanges due to a change in the drive voltage is extremely large at 120milliseconds, as shown in FIG. 9, and the efficiency is further reduced.Even with switching-mode amplification at a comparatively low frequency,a minimum of one cycle of about several milliseconds is required, whichis a common oscillation cycle. Problems are therefore encountered incases in which output power cannot be controlled with high precisionover time, and, at worst, the manufactured products themselves aredamaged and become defective.

The present invention was devised in view of such problems, and anobject thereof is to provide a high-frequency power supply circuit inwhich a simple configuration can be used to regulate and control outputpower with high precision over time in switching-mode amplification foroutputting such high frequencies.

Means for Solving these Problems

In order to solve the problems described above, the high-frequency powersupply circuit according to a first aspect of the present invention ischaracterized in comprising:

a basic drive square wave generation circuit unit for generating a basicdrive square wave having an output frequency outputted from ahigh-frequency power supply circuit; a differentiation signal generationcircuit unit for generating a front edge or rear edge differentialsignal of the generated basic drive square wave; a vibrator circuit unithaving a square wave signal generator for outputting a square wavesignal having a signal width within a time period corresponding to ahalf cycle of the output frequency upon input of a trigger signal froman external source, and signal width control circuits for variablycontrolling the signal width of the square wave signal on the basis of acontrol signal for controlling power output based on the outputfrequency; and a switching amplification circuit unit for amplifying anamplification source signal based on an output signal from the vibratorcircuit unit; the differential signal being generated by thedifferential signal generation circuit unit is used as a trigger signalin the vibrator circuit unit.

According to this aspect, in the vibrator circuit unit, the input of thedifferential signal is used as a trigger for the amplification sourcesignal, a square wave signal is generated having a signal width shorterthan a half cycle of the output frequency having an output time periodbased on the control signal, and the amplification source signal isamplified in the switching amplification circuit unit. Therefore, evenif the output frequency is high, the signal width of the amplificationsource signal can be varied according to the control signal with asimple configuration, and, consequently, the regulation of the outputpower from the high-frequency power supply circuit amplified by theswitching amplification circuit can be controlled precisely over timewith a simple configuration.

The high-frequency power supply circuit according to a second aspect ofthe present invention is the high-frequency power supply circuitaccording to the first aspect, characterized in that:

the square wave signal generator comprises a first reversing unit forinitiating reverse output of an input signal upon the input of thedifferential signal; and the signal width control circuit has a secondreversing unit for reversing the output signal from the first reversingunit and inputting the reversed signal to the first reversing unit, anda time constant circuit unit whereby the output signal outputted fromthe second reversing unit is blocked from being inputted to the firstreversing unit within a time period determined by a time constant thatvaries according to the control signal.

According to this aspect, the signal width control circuit can beconfigured in a simple configuration by using the monostable vibratorbased on a DC-AC link as the vibrator circuit unit. Therefore, there isa greater degree of freedom in the circuit design, and a vibratorcircuit unit having satisfactory precision with a simple configurationcan be obtained.

The high-frequency power supply circuit according to a third aspect ofthe present invention is the high-frequency power supply circuitaccording to the second aspect, characterized in that:

the first reversing unit is formed from a multi-input transformationlogic gate circuit.

According to this aspect, the first reversing unit 10 is formed using,e.g., a NAND gate or another such multi-input transformation logic gatecircuit that can operate at higher speeds than a common MSImultivibrator, whereby a square wave signal of a shorter signal widthcan be generated, and the range of controllable output power can befurther increased.

The high-frequency power supply circuit according to a fourth aspect ofthe present invention is the high-frequency power supply circuitaccording to any of the first through third aspects, characterized inthat:

the square wave signal generator outputs a square wave signal having asignal width of at least half or less of one cycle time during thesignal propagation delay times of at least two logic gates or fewer inone cycle time of the output frequency.

According to this aspect, since the signal width can be varied with eachcycle of output frequency, the output power within the same cycle can becontrolled with maximum precision over time.

The high-frequency power supply circuit according to a fifth aspect isthe high-frequency power supply circuit according to any of the firstthrough fourth aspects, characterized in comprising:

a logic gate circuit for receiving input of the basic drive square waveand an output signal from the vibrator circuit unit, and extracting theinputted basic drive square wave according to the inputted output signalfrom the vibrator circuit unit; wherein the switching amplificationcircuit unit amplifies the output signal from the logic gate circuit asthe amplification source signal.

According to this aspect, the signal width of an amplification sourcesignal can be prevented from reversing, and disturbance can be preventedfrom being caused by the reversing of the signal width (reversed duty).

The high-frequency power supply circuit according to a sixth aspect ofthe present invention is the high-frequency power supply circuitaccording to the fifth aspect; characterized in comprising:

a delay circuit for delaying the basic drive square wave inputted to thelogic gate circuit within the signal propagation delay time period inthe vibrator circuit unit.

According to this aspect, it is possible to avoid drawbacks in which thesignal width of the amplification source signal extracted by the logicgate circuit becomes shorter in proportion to the signal propagationdelay time.

The high-frequency power supply circuit according to a seventh aspect isthe high-frequency power supply circuit according to any of the firstthrough sixth aspects, characterized in that:

the time constant circuit unit has, as a time constant control element,a field-effect transistor (FET), a Cds element, a variable-capacitancediode, or a combination thereof.

According to this aspect, the time constant does not readily fluctuatein large amounts over time, and stable and continuous control cantherefore be achieved using the control signal inputted to the timeconstant circuit unit.

The high-frequency power supply circuit according to an eighth aspect isthe high-frequency power supply circuit according to any of the firstthrough seventh aspects, characterized in that:

the basic drive square wave generation circuit has a double-frequencygeneration circuit for generating a double frequency of the basic drivesquare wave; and the double frequency generated by the double-frequencygeneration circuit is used to generate a basic drive square wave havinga duty ratio of approximately 50%.

According to this aspect, a basic drive square wave having a duty ratioof about 50% can be generated with a high degree of precision.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit structure diagram showing an embodiment of thehigh-frequency power supply circuit of the present invention;

FIGS. 2( a) through (e) are flowcharts showing the timing of varioussignals in the high-frequency power supply circuit in the embodiment inFIG. 1;

FIG. 3 is a diagram showing the configuration of the high-frequencypower supply circuit in an example of the present invention;

FIG. 4 is a circuit structure diagram showing the high-frequency powersupply circuit of another aspect;

FIG. 5 is a diagram showing the configuration of a conventional powersupply circuit;

FIG. 6 is a drawing showing the configuration of a high-frequency powersupply circuit of another aspect;

FIG. 7 is a drawing showing the configuration of a high-frequency powersupply circuit of another aspect;

FIG. 8 is a diagram showing the measurement screen of an oscilloscopethat has measured the control speed of a high-frequency power supplycircuit in an example of the present invention; and

FIG. 9 is a diagram showing the measurement screen of an oscilloscopethat has measured the control speed of a conventional power supplycircuit.

KEY

-   -   1 Basic operation signal generator    -   2 Double-frequency generation circuit    -   3 Waveform rectification circuit    -   4 Divided frequency generation circuit    -   5 Basic drive square wave generation circuit unit    -   9 (Rear edge) differentiation circuit unit    -   10 First reversing unit    -   11 Reversing unit    -   12 Time constant circuit unit    -   12 E-class amplifier    -   12 Time constant circuit unit    -   13 Delay circuit unit    -   14 AND gate circuit    -   15 Monostable multivibrator    -   Q1 Field-effect transistor (FET)    -   IC₂ NAND gate circuit

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention are described hereinbelow.

To describe the embodiments of the present invention with reference tothe drawings, first, FIG. 1 is a circuit structure diagram showing theconfiguration of the high-frequency power supply circuit of the presentembodiment.

The high-frequency power supply circuit of the present embodiment isconfigured from a basic drive square wave generation circuit unit 5 forgenerating a basic drive square wave, which is a square wave having aduty ratio of about 50% and having the same frequency as the outputfrequency outputted from the high-frequency power supply circuit; adifferentiation circuit unit 9 for generating a front-edge differentialsignal of the basic drive square wave generated by the basic drivesquare wave generation circuit unit 5; a monostable multivibrator 15composed of a first reversing unit 10 to which the front-edgedifferential signal generated by the differentiation circuit unit 9 isinputted, a second reversing unit 11 for reversing and outputting theoutput signal from the first reversing unit 10, and a time constantcircuit unit 12 for variably controlling the time in which the outputsignal from the second reversing unit 11 is inputted to the firstreversing unit 10; a delay circuit unit 13 whereby the basic drivesquare wave generated by the basic drive square wave generation circuitunit 5 is delayed by the signal propagation delay time in the firstreversing unit 10; an AND gate circuit 14, which is a logic gate circuitin the present invention and to which the basic drive square wavedelayed by the delay circuit unit 13 and the output signal from thefirst reversing unit 10 are inputted; and an E-class amplifier 6, whichis a switching amplification circuit unit in the present invention foramplifying the amplification source signal outputted from the AND gatecircuit 14, as shown in FIG. 1.

The basic drive square wave generation circuit unit 5 of the presentembodiment is also configured from a basic operation signal oscillator1, a double-frequency generation circuit 2, a waveform rectificationcircuit 3, and a divided frequency generation circuit 4, as shown inFIG. 1.

This basic operation signal generator 1 can be an oscillator thatoutputs a high-frequency signal of 13.56 MHz if the output frequency is13.56 MHz, the output frequency being specifically the frequency of thehigh-frequency output of a high-frequency power supply circuit, e.g.,the previously described frequency of the high-frequency output, whichis a frequency equal to or greater than the megahertz range and whichcannot be controlled by a thyristor. The basic drive signal, which is ahigh-frequency signal generated by the basic operation signal generator1, is doubled to a frequency of 27.12 MHz by a conventional doublefrequency circuit.

The basic drive signal having a doubled frequency of 27.12 MHz isappropriately amplified in amplitude by an amplifying transistor (notshown), fed to the waveform rectification circuit 3, and shaped to asquare wave of 27.12 MHz. A square wave generation circuit normally usedin digital circuits or the like, i.e., a circuit that uses a reversingunit in multiple stages (for example, two stages), can be satisfactorilyused as the waveform rectification circuit 3.

The basic drive signal shaped in the waveform rectification circuit 3into a square wave having a doubled frequency of 27.12 MHz is suppliedto the divided frequency generation circuit 4 composed of, e.g., a pulsecounter or the like; and square waves divided by two into frequencies of13.56 MHz, or square wave divided by eight into frequencies of 3.39 MHzare generated according to the output frequency. In the exampledescribed hereinafter, the halved frequencies of 13.56 MHz are used inorder to bring the output frequency to 13.56 MHz.

Square waves generated by the basic drive square wave generation circuitunit 5 are thus generated based on the doubled frequency square waves,producing basic drive square waves (13.56 MHz) as square waves having aduty ratio of about 50%, as shown in FIG. 2. Some of these waves aresupplied to the AND gate circuit 14 via the delay circuit unit 13, andothers are supplied to the differentiation circuit unit 9, are changedto front-edge differential signals, and are thereby used as triggersignals for the monostable multivibrator 15.

In the monostable multivibrator 15 used in the present embodiment, acontrol signal for controlling the output power is inputted to the timeconstant circuit unit 12, and the time constant is varied according tothis control signal, whereby a signal of a short pulse width isoutputted to the AND gate circuit 14 by a reduction in the time constantin cases in which a control signal for reducing the output power isinputted, and a signal of a long pulse width is outputted to the ANDgate circuit 14 by an increase in the time constant in cases in which acontrol signal for increasing the output power is inputted.

In the monostable multivibrator 15, as shown in FIG. 1, two reversingunits are linked by an AC-DC link, and the first reversing unit 10 usedherein must be able to operate at: a high speed and be capable ofoutputting a square wave having a pulse width (signal width) shorterthan about 36.8 nanoseconds, which is half of one cycle of 73.7nanoseconds, as shown in FIG. 2, provided the half cycle of thehigh-frequency output frequency, that is, the output frequency, is 13.56MHz, as shown in FIG. 1. A reversing unit in which a NAND gate circuitIC₂ is used as the actual circuit in the example described hereinafteras shown in FIG. 3 may be used as the first reversing unit 10.

Thus, using a NAND gate circuit IC₂ makes it possible to output squarewaves having pulse widths that are shorter and more precise, because thelogic gate circuits allow for faster operation than common MSImultivibrators. With the pulse widths (signal width) formed in the NANDgate circuit IC₂ and outputted from the first reversing unit 10, thebasic drive square wave is extracted in the AND gate circuit 14 (IC₄ inFIG. 3) to create an amplitude source signal. Therefore, the shorterthese pulse widths, the smaller the size of the minimum pulse width ofthe amplitude source signal; i.e., the size of the output powercontrolled by the pulse widths. Consequently, the range of controllableoutput power can be made larger, the minimum units that can becontrolled within a variable range are smaller, and more precise outputcontrol can be achieved.

In the example in FIG. 3 described hereinafter, a NAND gate circuit IC₂is used as the first reversing unit 10, but the present invention is notlimited to this option alone, and reversing units capable of high-speedoperation based on other configurations may also be used.

Since the second reversing unit 11 merely reverses the output of thefirst reversing unit 10, the second reversing unit 11 can be a unit thathas relatively few propagation delays and can operate at the outputfrequency level.

The time constant circuit unit 12 constituting the monostablemultivibrator 15 may be a time constant circuit normally used as a timeconstant circuit unit and configured from a capacitor (C) and variableresistance (R). With a time constant circuit using a capacitor (C) andvariable resistance (R), however, the time constant is apt to varygreatly over time, and it is difficult to achieve stable continuouscontrol. Therefore, in the example shown in FIG. 3, a field-effecttransistor (FET) Q₁ in which the time constant does not vary greatlyover time, and in which power signals can be used as control signals, isused as the time constant control element. The grounding of the R inFIG. 1 is high-frequency grounding.

Operation of the high-frequency power supply circuit of the presentexample shown in FIG. 1 is described below by using the signal forms(timing) of the sections shown in FIG. 2. A basic drive square wave(13.56 MHz) having a duty ratio of about 50% is generated in the basicdrive square wave generation circuit unit 5, as shown in FIG. 2( a).

The generated basic drive square wave is inputted to the differentiationcircuit unit 9, and is thereby converted to a front-edge differentialsignal whose front edge alone is extracted, as shown in FIG. 2( b). Thefront-edge differential signal is inputted as a trigger signal to thefirst reversing unit 10.

The first reversing unit 10 begins signal output upon the input of thefront-edge differential signal from the differentiation circuit unit 9,and signal output is ended at the moment in time when the reversedoutput of this signal output by the second reversing unit 11 is inputtedto the first reversing unit 10 due to the passage of time based on thetime constant set by the time constant circuit unit 12. In other words,at the moment in time when the front-edge differential signal isinputted, the first reversing unit 10 outputs a signal of a pulse width(signal width) corresponding to a time period based on the time constantset by the time constant circuit unit 12, as shown in FIG. 2( c).

Since a temporal delay, i.e., a signal propagation delay time, occursfrom the time the front-edge differential signal is inputted until thetime the signal is actually outputted as shown in FIG. 2( c), an outputsignal delayed by the signal propagation delay time is inputted to theAND gate circuit 14. When a basic drive square wave is inputteddirectly, the signal width of the basic drive square wave extracted inthe AND gate circuit 14 is shorter by the signal propagation delay time.Therefore, in order to avoid this problem, the basic drive square waveis sent through the delay circuit unit 13 for delaying the basic drivesquare wave by the signal propagation delay time in the first reversingunit 10, whereby both signals inputted to the AND gate circuit 14 aresynchronized, and an amplitude source signal corresponding to the signalwidth of the first reversing unit 10 can be obtained as shown in FIG. 2(e).

Thus, the signal propagation delay time in the first reversing unit 10has a length approximate to that of one cycle time of the outputfrequency, and in cases in which the length exceeds (is greater than)one cycle time, or in cases in which the length (size) of the minimumpulse width (signal width) that can be outputted in the first reversingunit 10 is approximate to the length of one cycle time of the outputfrequency, it is difficult to control the output on the basis of thesignal width within the same cycle of the basic drive square wave.Therefore, the first reversing unit 10, which is the square wave signalgenerator in the present invention, is preferably a unit that can outputa square wave signal having a signal width of at least half or less ofone cycle time during a signal propagation delay time of at least twologic gates or fewer in one cycle time of the output frequency.

In the present embodiment, the AND gate circuit 14 is used to achieveextraction from the basic drive square wave, whereby an excessive timeconstant (reversed duty ratio) as shown by the dashed lines in FIG. 2can be prevented. This is preferable because the signal width can bereversed, whereby damage the machinery and other problems can beprevented by reversing the control force. However, the present inventionis not limited to this option alone, and the output signal from thefirst reversing unit 10 may also be inputted unchanged as anamplification source signal to the E-class amplifier 6 without using theAND gate circuit 14, in which case the delay circuit unit 13 can beomitted.

EXAMPLE

FIG. 3 is a circuit diagram showing a circuit that has actually beenmanufactured. As described above, a NAND gate circuit IC₂ is used as thefirst reversing unit 10, and a capacitor C₁ and a drain-to-sourceresistance (R_(DS)) of a field-effect transistor (FET) Q₁ are used asthe time constant circuit unit 12.

In FIG. 3, a reversing circuit IC₁ is a circuit for reshaping theinputted basic drive square wave. This circuit may be omitted in casesin which the basic drive square wave is not adversely affected in thepropagation channel of the inputted basic drive square wave.

In the present example, the differentiation circuit unit 9 is configuredfrom R₁, R₂, and C₂; and the R₁ side is connected to Vd, whereby “1” asa HIGH state is inputted to the input 2 of the NAND gate circuit IC₂when no front-edge differential signals are being outputted, and “0” asa LOW state is inputted to the input 2 when front-edge differentialsignal are being outputted. Since the circuit element causes anoperation delay, the front-edge differential signal requires a timeconstant sufficient to maintain the LOW state of “0” until the input 1of the NAND gate circuit IC₂ becomes the LOW state of “0.”

In FIG. 3, IC₅ through IC₇ are delay units; the delay circuit unit 13 isformed by IC₅ through IC₇; IC₃ corresponds to the second reversing unit11; and IC₄ corresponds to the AND gate circuit 14.

In the present embodiment, using the field-effect transistor (FET) Q₁allows the electric potential of the input 1 of the NAND gate circuitIC₂ to reach the LOW state of “0” during a time period equal to the timeconstant composed of C₁ and the drain-to-source resistance (R_(DS))corresponding to the gate voltage when the front-edge differentialsignal is added to the input 1 of the NAND gate circuit IC₂ in a statein which the voltage signal is applied as a control signal to the gateof the FETQ₁. After the time period equal to the time constant haspassed, the electric potential of the input 1 of the NAND gate circuitIC₂ reaches the HIGH state of “1,” whereby the input state and timeperiod of the input 1 of the NAND gate circuit IC₂ can be controlled bythe voltage signal of the control signal, making it possible to achievecontinuous control that remains stable over time.

In the present embodiment, the NAND gate circuit IC₂ is used as thefirst reversing unit 10, thereby yielding a reversing unit that canproduce a pulse width sufficiently short to be used at 13.56 MHz. Todescribe the operation of this NAND gate circuit IC₂, the HIGH state of“1” is inputted, at the time of no output for front-edge differentialsignals, to the input 2 connected to the differentiation circuit unit 9configured from the R₁, the R₂, and the C₂ in the manner describedabove, and the other input 1 is also connected to the Vd via thefield-effect transistor (FET) Q₁, whereby the HIGH state of “1” isinputted, and the output of the NAND gate circuit IC₂ is therefore thelow state of “0.” When the threshold in the input 2 of the IC₂ isV_(IL), the relationship between R₁ and R₂ is Vd·R₂/(R₁+R₂)>V_(IL).

In this state, when the front-edge differential signal is outputted;i.e., when the LOW state of “0” is inputted to the input 2, the outputof the NAND gate circuit IC₂ is brought to the HIGH state of “1.”

The output of the HIGH state of “1” causes the LOW state of “0,” whichis the reversed output, to be outputted from the IC₃ corresponding tothe second reversing unit 11, where by the output of the NAND gatecircuit IC₂ is maintained at the HIGH state after the start of the inputof the LOW state of “0” to the input 1 (immediately followingdifferential signal input), even if the front-edge differential signalis not being outputted; i.e., even if the output is the LOW state of“0.”

The electric potential of the input 1 of the IC₂ returns back to theHIGH state of “1” after a time period R_(DS)·C₁ (sec) corresponding tothe gate power of the field-effect transistor (FET) Q₁ has passed,whereby the electric potentials of both the input 1 and the input 2 arebrought to the HIGH state of “1,” and the output of the NAND gatecircuit IC₂ is therefore brought to the LOW state of “0.” Therefore,upon input of the front-edge differential signal, a square wave signalhaving a signal width within a time period corresponding to a half cycleof the output frequency of 13.56 MHz, which is set in the time constantcircuit unit 12, is outputted from the NAND gate circuit IC₂, and thefirst reversing unit 10 formed by the NAND gate circuit IC₂ is thereforeequivalent to the square wave signal generator in the present invention.

On the basis of a control signal for controlling the power output, thetime constant circuit unit 12 of the monostable multivibrator 15configured from the field-effect transistor (FET) Q₁ and othercomponents performs variable control of the pulse width (signal width)outputted from the NAND gate circuit IC₂ constituting the firstreversing unit 10, which is the square wave signal generator in thepresent invention. The time constant circuit unit 12 is thereforeequivalent to the signal width control circuit in the present invention.

As described above, in cases in which the pulse width (signal width)outputted from the NAND gate circuit IC₂ and varied according to thecontrol signal; e.g., in cases in which the pulse width (signal width)in question is half of the pulse width (signal width) of the basic drivesquare wave, an amplification source signal having a pulse widthapproximately half (50%) of the pulse width (signal width) of the basicdrive square wave is outputted from the AND gate circuit 14 to theE-class amplifier 6 and amplified, and the output is thereby narrowed.Furthermore, in cases in which the pulse width (signal width) outputtedfrom the pertinent NAND gate circuit IC₂ is one third of the pulse width(signal width) of the basic drive square wave, an amplification sourcesignal having a pulse width approximately one third (33%) of the pulsewidth (signal width) of the basic drive square wave is outputted fromthe AND gate circuit 14 to the E-class amplifier 6 and amplified, andthe output is thereby narrowed.

As described above, according to the high-frequency power supply circuitof the present example, in the monostable multivibrator 15 that servesas a vibrator circuit unit, the input of the front-edge differentialsignal is used as a trigger for the amplification source signal, asquare wave signal is generated that has a signal width shorter than ahalf cycle of the output frequency and that has an output time periodbased on the control signal, and the amplification source signal isamplified in the switching amplification circuit unit. Therefore, evenat a high output frequency, the signal width of the amplification sourcesignal can be varied according to the control signal by using a simpleconfiguration, and, consequently, the regulation of the output powerfrom the high-frequency power supply circuit amplified by the E-classamplifier 6, which is a switching amplification circuit, can becontrolled with high precision over time by using a simpleconfiguration. Specifically, the regulation can be controlled with anaccuracy of about 200 nanoseconds, as shown in FIG. 8.

According to the high-frequency power supply circuit of the presentexample, the signal width control circuit can be provided with a simpleconfiguration that has the second reversing unit and the time constantcircuit unit 12. This can be achieved by using the monostable vibratorbased on a DC-AC link as the vibrator circuit unit. Therefore, there isa greater degree of freedom in the circuit design, and a vibratorcircuit unit having satisfactory precision and a simple configurationcan be obtained.

According to the high-frequency power supply circuit of the presentexample, the first reversing unit 10 is formed using a NAND gate circuitIC₂ that can operate at higher speeds than can a common MSImultivibrator, whereby a square wave signal of a shorter signal widthcan be generated, and the range of controllable output power can befurther increased.

According to the high-frequency power supply circuit of the presentexample, since the signal width can be varied with each cycle of outputfrequency, the output power within the same cycle can be controlled withmaximum precision over time.

According to the high-frequency power supply circuit of the presentexample, the AND gate circuit 14 is used, whereby the signal width of anamplification source signal can be prevented from reversing, anddisturbance can be prevented from being caused by the reversing of thesignal width (reversed duty).

According to the high-frequency power supply circuit of the presentexample, the delay circuit unit 13 is used, whereby it is possible toavoid drawbacks in which the signal width of the amplification sourcesignal extracted by the AND gate circuit 14 as the logic gate circuitbecomes shorter in proportion to the signal propagation delay time.

According to the high-frequency power supply circuit of the presentexample, since a field-effect transistor (FET) is used as the timeconstant control element, the time constant does not readily fluctuatein large amounts over time, and stable and continuous control cantherefore be achieved using the control signal inputted to the timeconstant circuit unit.

According to the high-frequency power supply circuit of the presentexample, since the basic drive square wave is generated using a doublefrequency, a basic drive square wave having a duty ratio ofapproximately 50% can be generated with a high degree of precision.

Examples of the present invention were described above based on thedrawings, but the specific configuration is not limited to theseexamples, and the present invention includes modifications and additionswithin a range that does not deviate from the scope of the presentinvention.

For example, in the examples described above, a reference operationsignal was generated having the same frequency (13.56 MHz) as thehigh-frequency output of the high-frequency power supply circuit, and adouble frequency (double wave: 27.12 MHz) of the reference operationsignal was generated by the double-frequency generation circuit 2, butthe present invention is not limited to this option alone. Anotheroption is to not use this double-frequency generation circuit 2, but todirectly generate a double frequency of the reference operation signalby using, e.g., a 27.12-MHz oscillator.

In the examples described above, a double wave was used as the doublefrequency, but the present invention is not limited to this optionalone, and another possibility is to use a more than double wave, suchas a quadruple or octuple wave, and to generate a basic drive squarewave or a control square wave which is a square wave having a duty ratioof approximately 50%.

In the examples described above, the basic drive square wave wasgenerated using a double frequency, but the present invention is notlimited to this option alone, and another possibility is to generate thebasic drive square wave without using a double frequency.

In the examples described above, the AND gate circuit 14 was used as alogic gate circuit, but the present invention is not limited to thisoption alone, and a multi-input logic gate circuit (NAND gate circuit orOR gate circuit) having a suitable and appropriate AND operation circuitfunction based on the control scheme can be used as the logic gatecircuit.

In the examples described above, a low pass filter (LPF) 7 is provided,making it possible to achieve output in the for of both sine waves andpulses, but the present invention is not limited to this option alone,and either one of these outputs alone may be used.

In the examples described above, the delay circuit unit 13 was used, butthe present invention is not limited to this option alone, and the delaycircuit unit 13 may be omitted in cases in which the output frequency iscomparatively low and the delay propagation time period in the firstreversing unit 10 is small enough for the signal width of the outputfrequency.

In the examples described above, a differential signal is used and afront-edge differential signal is inputted as a trigger signal to thefirst reversing unit 10, but the present invention is not limited tothis option alone. For example, a rear-edge differentiation circuit unit9′ may be used to input a rear-edge differential signal to the firstreversing unit 10, and a third reversing unit 10′, which is the samereversing unit as the first reversing unit 10, may be used as the delaycircuit unit 13, as shown in FIG. 4, thereby obviating the need to matchthe two delay propagation time periods inputted to the AND gate circuit14.

In the examples described above, the time constant circuit unit 12 basedon the field-effect transistor (FET) Q₁ was given as an example of atime constant control element, but the present invention is not limitedto this option alone, and a CdS photocell, a variable-capacitance diode,or the like can be used as the time constant control element.

Specifically, in cases in which a variable-capacitance diode is used,the operation as such is the same as that of the circuit in FIG. 3except for the use of electrostatic capacitance to vary the timeconstant as shown in FIG. 6. Cd in the circuit in FIG. 6 is theelectrostatic capacitance of the variable-capacitance diode. As isconventionally known, C1 and C3 are direct current blockers, and arecommonly set so that C₁ and C₃ are much greater than Cd. The timeconstant is determined by R and Cd. FIG. 6 is an example of using themost common variable-capacitance diode, and FIG. 7 shows, as an exampleof application, and example in which a variable-capacitance diodespecifically adapted for the present invention is used.

In the examples described above, 13.56 MHz, which is a frequency thatcannot be controlled with a thyristor or the like, was used as anexample of the output frequency, but the present invention is notlimited to this option alone, and it is apparent that the high-frequencypower supply circuit of the present invention can be used with an outputfrequency of several hundred kilohertz that can be used by a thyristor.

In the examples described above, a monostable multivibrator circuithaving AC-DC links was used as the vibrator circuit unit, but thepresent invention is not limited to this option alone. Anotherpossibility is to use a vibrator circuit unit that can output a squarewave signal having a signal width within a time period equivalent to ahalf cycle of the required output frequency upon the input of a triggersignal from an external source, and that can variably control the signalwidth of the square wave signal on the basis of a control signal.

1. A high-frequency power supply circuit characterized in comprising: abasic drive square wave generation circuit unit for generating a basicdrive square wave having an output frequency outputted from thehigh-frequency power supply circuit; a differentiation signal generationcircuit unit for generating a front edge or rear edge differentialsignal of the generated basic drive square wave; a vibrator circuit unithaving square wave signal generator for outputting a square wave signalhaving a signal width within a time period corresponding to a half cycleof the output frequency upon input of a trigger signal from an externalsource, and signal width control circuits for variably controlling thesignal width of said square wave signal on the basis of a control signalfor controlling power output frequency; and a switching amplificationcircuit unit for amplifying an amplification source signal based on anoutput signal from the vibrator circuit unit; the differential signalbeing generated by the differential signal generation circuit unit isused as a trigger signal in said vibrator circuit unit.
 2. Thehigh-frequency power supply circuit according to claim 1, characterizedin that: said square wave signal generator comprises a first reversingunit for initiating reverse output of an input signal upon the input ofsaid differential signal; and said signal width control circuit has asecond reversing unit for reversing the output signal from the firstreversing unit and inputting the reversed signal to the first reversingunit, and a time constant circuit unit whereby the output signaloutputted from the second reversing unit is blocked from being inputtedto the first reversing unit within a time period determined by a timeconstant that varies according to said control signal.
 3. Thehigh-frequency power supply circuit according to claim 2, characterizedin that said first reversing unit is formed from a multi-inputtransformation logic gate circuit.
 4. The high-frequency power supplycircuit according to claim 1, characterized in that the square wavesignal generator outputs a square wave signal having a signal width ofat least half or less of one cycle time during the signal propagationdelay times of at least two logic gates or fewer in one cycle time ofthe output frequency.
 5. The high-frequency power supply circuitaccording to claim 1, characterized in compromising: a logic gatecircuit for receiving input of said basic drive square wave and anoutput signal from said vibrator circuit unit, and extracting theinputted basic drive square wave according to the inputted output signalfrom the vibrator circuit unit; wherein said switching amplificationcircuit unit amplifies the output signal from said logic gate circuit assaid amplification source signal.
 6. The high-frequency power supplycircuit according to claim 5, characterized in comprising a delaycircuit for delaying the basic drive square wave inputted to said logicgate circuit within the signal propagation delay time period in saidvibrator circuit unit.
 7. The high-frequency power supply circuitaccording to claim 1, characterized in that aid time constant circuitunit has, as a time constant control element, a field-effect transistor(FET), a Cds element, a variable-capacitance diode, or a combinationthereof.
 8. The high-frequency power supply circuit according to claim1, characterized in that: said basic drive square wave generationcircuit has a double-frequency generation circuit for generating adouble frequency of said basic drive square wave; and the doublefrequency generated by the double-frequency generation circuit is usedto generate a basic drive square wave having a duty ratio ofapproximately 50%.